Since the existence and importance of circadian rhythms in human beings and animals is known, products have been developed that try to use this knowledge. The US 2005/0015122 discloses for example methods for controllably adjusting the circadian pacemaker cycle of a subject using light through application of model-based predictive control techniques.
EP 2 656 782 A1 discloses a device consisting of at least one body position and activity sensor, at least one peripheral temperature sensor and at least one light sensor, configured to provide information on the circadian system status and the sleep-wake status of an individual based on the data obtained from said sensors. It can be placed on the wrist of the subject, or on the subject's arm. The device may also include a blood pressure sensor. This device may be used in general studies of the human circadian system and, more specifically, for the study of sleep-wake and blood pressure rhythms.
WO 2012/056342 A2 discloses a method for determining a feature of the circadian rhythm of the subject, comprising measuring a first input signal indicating a cardiac function of the subject, measuring at least one second input signal indicating the activity of the subject, combining the first input signal and the second input signal to a periodic output signal representing the circadian rhythm of the subject, and determining at least one feature of this periodic output signal.
The article “Addition of a non-photic component to a light-based mathematical model of the Human Circadian Pacemaker” by St. Hilaire M. A. et. al., Journal of Theoretical Biology, vol. 247, pp. 583-599 (2007) discloses a modified light-based circadian mathematical model to reflect evidence from studies that the sleep-wake cycle and/or associated behaviors have a non-photic effect on the circadian pacemaker. The sleep-wake cycle and its associated behaviors provides a non-photic drive on the circadian pacemaker that acts both independently and concomitantly with light stimuli.
The article “Actigraphy: A Means of Assessing Circadian Patterns in Human Activity” Brown A. C. et. al., Chronobiology International, vol. 7, no. 2, pp. 125-133 (1990) discloses the continuous monitoring of twenty-three diurnally active (0705-2333), healthy persons between 22 and 54 yrs of age and without history of sleep abnormality for 120 consecutive hr (five days) by wrist actigraphy. Circadian rhythms of high amplitude were detected by cosinor analysis for each participant and for the groups of 10 males and 13 females with the average span of heightened activity timed between ˜1330 and 1605. The circadian peak-trough difference in wrist movement was marked, equaling approximately 75% of the 24-hr mean level. In 19 of 23 participants, the 24•hr mean of wrist activity varied between 140-180 movements/min, with four persons exhibiting lesser means of 110-140 movements/min. With respect to the daytime span of activity, the mean wrist movement of individual participants ranged from 155-265 movements/min, with the majority (20/23) varying between 185-245 movements/min. During nocturnal sleep the mean wrist activity level was quite low, varying between individuals from 5 to 25 movements/min for 21 of 23 persons. Wrist actigraphy proved to be well-accepted and was a most reliable means of monitoring aspects of body movement during activity and sleep in ambulatory persons adhering to usual life habits and pursuits.